Kris Jenner -- Here's My Proof ... A Spider Made Gave Me a Fat Lip (PHOTO)

Kris Jenner just schooled us and anyone else who thought her "fat lip" excuse for cancelling a TV appearance was fake ... she says it was real, and serious.

We got this pic of Kris taken Monday morning, around the time she called producers of "Bachelor In Paradise: After Paradise" and cancelled her scheduled appearance, saying her lip blew up and she was not camera ready.

Kris says the culprit was most likely a spider so she had her room sprayed by an exterminator. The swelling was serious enough for a doctor to prescribe 4 different meds.

As for showing up Tuesday night at Nobu and looking just fine, Kris made it clear to friends and family it took 18 hours for the swelling to go down.

It's not the first time Kris' lips blew up ... she had an allergic reaction to food in the Dominican Republic a few years back.